Instead of the Open with Mail menu, can I define to open the email message with Entourage? I don’t need or have the regular Mail program setup - only using Entourage, and from what I can see there is no way for me to search for an old email then either reply or forward it to someone with a click or two.
Have you tried using the Reply to Message command in EagleFiler? That should, in one click, open the reply window in your chosen e-mail client.
To change which application opens when you double-click a message, find a .eml file (for example by dragging a message from Entourage to the desktop). Get Info on it in the Finder, change the Open With to Entourage, and then click Change All.